In U.S. Pat. No. 4,580,957 a bearing arrangement for a wave generator capable of eccentrically deflecting a flexible ring of a rotary piston engine was disclosed. The bearing arrangement included a pair of rolling discs arranged side by side and supported on a drive shaft through eccentrics which were pivotable against each other. A flexible ring was engaged by the radially external face of each of the rolling discs. The flexible ring constituted the engine piston ring and was forced against the inner face of a cylinder wall. The piston ring was flexed or deflected through rolling contact between its inner face and the external faces of the rolling discs.
Among the problems encountered with such arrangement was the fact that the flexible piston ring accumulated foreign matter including combustion byproducts on its inner face. Such accumulations were in some instances due to engine ventilation.
Further, when a comparatively soft material was utilized for the flexible piston ring, such as austintite, the flexible piston ring deformed, i.e. became wavy, in the rolling contact area between the external faces of the rolling discs and the inner face of the flexible piston ring. The deformation was primarily due to flexing in the exhaust suction direction. In view of the requirements for sealing the cylinder and piston ring in the engine, piston ring deformations were undesirable.
In addition, the disclosed bearing arrangement presented difficulties in connection with the balancing of the comparatively large revolving masses. Balancing requirements presented increased manufacturing costs.
Another wave generator bearing arrangement has been disclosed in U.S Pat. No. 4,003,272 in conjunction with a harmonic drive planetary gear. The invention therein disclosed included three identical rolling discs positioned side by side. The radially external faces of the discs contacted the inner face of a flexible splined planet wheel.
To support the rolling discs, identical roller bearings were provided between each rolling disc and interiorly positioned eccentric rings, also arranged side by side. The bearing assembly was relatively long in an axial direction and was thus not practical in applications with limited space requirements. Further, as a result of an endless bearing ring which extended over the same axial length as the flexible planet wheel, relatively large radial forces and concomitant bearing loads were generated.
In addition, since the radial force exerted on the central rolling disc was twice that exerted on each of the lateral rolling discs, the central bearing received twice the load than the bearings which supported the lateral rolling discs. As a result, the useful life of the wave generator was determined by that of the central bearing.
Also, because the three rolling bearings were of identical construction, assembly of the bearing system required a three part design of the driving eccentric. In addition, relatively high system imbalance resulted due to the fact that eccentric rings, rolling bearings and rolling discs of identical design were employed. Such system imbalanced resulted in additional balancing expenses and relatively high manufacturing costs.